1. Field of the Invention
This invention relates to helicopters and, more specifically, to folding the blades of the helicopter.
2. Description of the Related Art
While the flight capabilities of helicopters makes them effective vehicles for a wide variety of flight missions, the utility of helicopters in certain circumstances may be limited by the overall structural envelopes thereof. To provide the power required to support the flight capabilities of helicopters, the main rotor assemblies of helicopters, incorporate a plurality of main rotor blades having large radial dimensions. The large radial dimensions of helicopter rotor assemblies results in helicopters having large structural envelopes that occupy an inordinate amount of space. The large structural envelopes of helicopters may limit their utility in some circumstances.
For example, helicopters utilized for maritime flight operations may be required to conduct operations from ships for extended periods of time. Shipboard space is generally at a premium, and the large structural envelopes of helicopters means that stowage of helicopters during periods of non-use requires a large allocation of such limited space. The same concern arises for helicopters operating from oceanic oil rigs wherein helicopters are stowed during periods of non-use. In addition to space limitations arising from the structural envelopes of helicopters due to the main rotor assemblies, the main rotor assemblies of stowed helicopters that are exposed to the environment are vulnerable to wind gusts. Furthermore, strategic and tactical considerations in the military utilization of helicopters has led to a requirement for helicopters having main rotor assemblies that may be readily reconfigured for rapid deployment, routine transport, and/or stowage through reduction in the structural envelopes of the helicopters.
Several options are available to reduce the structural envelopes of helicopters to facilitate rapid deployment, routine transport, stowage, and/or to reduce the vulnerability thereof to environmental conditions. One option is to design the main rotor assemblies of helicopters so that the main rotor blades may be removed from the rotor hub assembly. While this is a viable solution in some circumstances, it should be appreciated that such main rotor blade assemblies may be unnecessarily complex. In addition, it should be appreciated that removal of the main rotor blades tends to be time consuming and labor intensive. Moreover, these same time constraints and labor requirements exist when the helicopter is reconfigured for subsequent flight operations. Further, removal of the main rotor blades may require rebalancing of the blades upon reattachment. Therefore, reduction of the structural envelope of helicopters by removal of the main rotor blades may not be the most viable option under some circumstances.
Another option available to reduce the structural envelopes of helicopters is to design the main rotor assemblies thereof so that the main rotor blades may be folded about the main rotor hub assembly. Main rotor blade folding operations may be implemented either automatically via hydraulic systems or manually. Automatically controlled blade folding operations require relatively extensive modifications to the main rotor assembly to incorporate the necessary mechanical apparatus to effectuate automatic blade folding. In addition, specialized software must be incorporated in the automatic flight control system to regulate automatic blade folding operations. Representative examples of such mechanical apparatus and specialized software are illustrated in U.S. Pat. Nos. 4,354,234, 4,284,387, and 3,743,441. Such mechanical apparatus unnecessarily increase the complexity of the main rotor assembly. In addition, such mechanical apparatus and software increases the overall system cost of the helicopter.
Manual blade folding operations, in contrast, generally require minimal mechanical modifications to the main rotor assembly, and do not generally require specialized software. In light of the minimal mechanical modifications required to incorporate blade folding capabilities in helicopter main rotor assemblies, this option represents a viable approach in a number of circumstances. For example, for maritime operations and oil rig use, manual blade folding operations may be effected with minimal manpower in a short period of time to reduce the overall structural envelope of helicopters. The modifications to the main rotor assembly required to accommodate manual blade folding operations result in only an incremental increase in the complexity of the main rotor assembly and the overall systems costs of the helicopter.
However, manual blade folding operations do pose a concern in terms of the pitch actuation system of the helicopter. The helicopter pitch actuation system is a relatively complex hydromechanical system comprised of a large number of precisely aligned, structurally and functionally interrelated components. Such components include the pilot's input (collective; cyclic), interconnecting mechanical linkages, hydraulic servo systems, a swashplate assembly (stationary; rotating), pitch control rods, and pitch control horns. It goes without saying that proper operation of the pitch actuation system is vital to safe and efficient helicopter flight operations. Proper operation of the pitch actuation system, in turn, requires precise alignment and functional interactions among the various elements of the hydromechanical system. Pilot inputs via the collective and cyclic controls must be accurately and systematically converted to repeatable pitch inputs to the main rotor blades via the pitch actuation system.
During blade folding operations, however, displacements may be induced into the main rotor blades being folded by wind gusts, loss of physical blade control, etc. Such displacements may be coupled into the pitch actuation system by means of the respective pitch control horns. Such coupled displacements may damage or degrade the pitch actuation system by disrupting the precise alignment and/or functional interactions among the various components of the hydromechanical pitch actuation system, thereby negatively impacting the accuracy and repeatability of the pitch actuation system. Increasing the concern vis-a-vis damage or degradation of the flight actuation system is the fact that such damage or degradation may occur to components of the hydromechanical system that are located within the helicopter fuselage, and as such, not readily visible during preflight checks prior to commencing flight operations.
Further, the main rotors blades are essentially air foils that during a manual folding operation may be hard to control by the personnel folding the blades. An example of main rotor blade has a center of gravity about 10 feet out from the hub and weighs approximately 170 pounds. Prior art discloses the use of a pole that is attached to the rotor blade tip such that a person may use the pole to guide the tip during the folding process.